The invention relates to an antenna for resonance heating of material.
A known antenna for radiation heating of material using resonance or harmonic excitation is disclosed in WO00/25552 entitled xe2x80x9cHeating Arrangementxe2x80x9d having a priority date of Oct. 27, 1998. The arrangement is made up of several surface antenna elements each of which consists of a carrier surface material and a radiation coating applied thereto that is delimited by means of two spaced, parallel electrical conductors having electrical contacts as antenna limiters. With this radiation coating, high-frequency electromagnetic radiation can be emitted from the antenna. Moreover, the process of heating by radiation from an antenna requires a harmonic generator that is coupled to two electrical conductors on the antenna surface element for excitation of the radiation coating so that an oscillatory spectrum within the range of the natural molecular frequencies of the matter to be heated can be emitted. Furthermore, a suitable radiation coating is specified in the foregoing disclosure, which generates a suitable radiation spectrum with the described excitation. In addition, a multiple arrangement of surface antenna elements is disclosed such that in a corner of a room twelve rectangular surface antenna elementsxe2x80x94four, each side by side, in three vertically positioned rowsxe2x80x94are arranged with small spacings and are electrically connected in parallel. The electromagnetic waves are created by means of a harmonic generator.
It has been shown that for the efficient heating of a room, for example, the surface antenna elements should have a relatively large area, the individual surfaces not being randomly enlargeable since the heating effect would then be reduced again. Accordingly, it is expedient to use the specified or a similar multiple arrangement of surface antenna elements. Control of the electrical supply wires is in the low voltage range, e.g. about 24 volts. Thus, in operation the relatively cool radiation coating of a surface antenna element can be touched without the risk of electric shock, i.e. touching is entirely non-critical. Surprisingly, however, it has been found that considerable potential differences may occur between the surface antenna elements of a multiple arrangement. In parallel connections, this might be due to the phase shifts of the oscillatory spectrums of the individual surface antenna elements. In the event that several surface antenna elements are within reach of a technician or a heating user, there is thus the risk of electric shock if two or more surface antenna elements are simultaneously touched. Although such electric shock is, as a rule, not dangerous or hazardous to health, it may be an extremely unpleasant experience. Until now, this problem has not been recognized within the state of the art and has not been described either. Accordingly, it is one object of the invention to develop basic heating by antenna radiation so that the risk of electric shocks is virtually eliminated. The foregoing objects are realized by the invention summarized below:
Briefly, the invention is an antenna radiation heater for heating material using resonance comprising a plurality of antenna elements, each having a carrier surface material and a radiation coating applied thereon which is delimited by two spaced parallel electrical conductors with electrical contact as antenna limiters and from which high-frequency electromagnetic radiation can be emitted; a harmonic generator coupled to the two electrical conductors of a surface antenna element for excitation of the radiation coating for the emission of an oscillation spectrum within the range of the natural molecular frequencies of the matter to be heated; and a radiation coating applied unilaterally onto the carrier surface material to form an element front facing the material heated and a contact protection layer applied on the radiation coating against contact which also permits the emission of the oscillation spectrum without any or at most with only minor attenuation.
In a further explanation of and first aspect of the invention, radiation coating is applied on one side on the carrier surface material and forms the first of the elements facing the material to be heated. Furthermore, a contact protection layer is applied to the radiation coating. The material of such a contact protection layer preferably is selected such that, on the one hand, the radiation coating is electrically insulated against contact and, on the other hand, the emission of the oscillatory spectrum is possible without any or at least only minor attenuation. The two properties of the radiation coating that are essential in this combination are that the coating acts as an electrical insulation layer to avoid electric shocks upon touching two elements, and that the coating allows for attenuation-free radiation or, at least, low-attenuation of the emission of the oscillatory spectrum.
According to a second aspect, the carrier surface material as the element""s reverse side should preferably also have electrical insulation properties; however, as opposed to the contact protection layer, it should either entirely or at least significantly attenuate the emission of the oscillatory spectrum. This will be achieved in that the radiation energy as a whole or at least a major part of it will be emitted via the element front which will result in a particularly energy saving heating of the material.
A suitable contact layer, according to a third aspect of the invention, having the above specified properties, may consist of an aqueous, finely dispersed, softener-free, medium viscosity copolymer dispersion of acrylic and methacrylic acid esters which advantageously has a solids concentration of approximately 50% and an average particle size of approximately 0.1 xcexcm.
Alternatively, a suitable contact layer according to a fourth aspect of the invention may consist of an aqueous, protective colloidal, medium viscosity polymer dispersion of vinyl acetate, versatic acid, vinyl ester and maleic acid di-n-butyl ester, advantageously having a solids concentration of approximately 50-55% and an average particle size of approximately 0.2 xcexcm.
The coating material of the radiation coating can be selected in a manner known in the art in accordance with the composition of a fifth aspect of the invention. The specified sulfonated oil here preferably consists of sulfonated ricinus oil and the specified phenols are advantageously carbonized phenols produced by cracking, or benzisothiazolinone is used. As a thinning agent, a solvent based on aromatics and/or alcohol and/or ester and/or ketone has proven to be advantageous whereas an inorganic and/or organic, monomeric and/or polymeric substance is particularly suitable as a dispersing agent. Insulating soot is suitable as an insulator, and the coating material should contain a thixotropy agent.
The radiation coating and the contact protection layer can be applied and produced by methods known per se. According to a sixth aspect, the radiation coating and/or after its firming up, the contact protection layer are produced, especially advantageously, by means of blade spreading. In particular, the amount of casein or, possibly, of polyacrylates in combination with a blade spreading method cause a radiation attenuation toward the element""s reverse side, especially if the radiation coating is applied to paper material. The contact protection layer is also expediently produced by blade spreading, with layer gauges of approximately 5-10 xcexcm regularly being sufficient for contact protection and, at that, still not causing any unfavorable attenuation of emission on the element""s front side.
In a manner known to those skilled in the art, a suitable excitation of the radiation coating according to a seventh aspect of the invention is possible such that the harmonic generator as a component of a control/regulating device comprises an electrical element whichxe2x80x94upon control with a control oscillationxe2x80x94shows a steep current speed increase in accordance with a steep rising curve and thus is suitable for producing a high harmonic proportion. The electrical element may be, for example, a Triac (bi-directional triode thyristor) or Doppel-MOS FET (Double metalonide-semiconductor-fill-effect-transitor) with the allocated electronic control components known to those skilled in the art. The resonance arrangement takes the required energy as needed from the connected electrical network, with the heating effect being at least partly controllable and/or adjustable by changing the amplitudes and/or the frequency of the oscillator control.
According to an eighth aspect, it is expedient to design the electrical conductors in a conventional manner as copper foil strips arranged in parallel. A covering of copper foil strips as known in the art as antenna limiters with an electrical insulating layer (see, for example, German Patent document DD 208 029) can also be realized. The electrical contact to the radiation coating is designed as a capacitive and/or inductive coupling.
The indicated contact protection is especially essential if, according to a ninth aspect, the multiple antenna surface elements are arranged within mutual reach, electrically connected in parallel and excitable by means of a harmonic generator. Even if several harmonic generators are used for the antenna surface elements, there is the risk of an electric shock due to the above-mentioned potential differences so that a contact protection with an electrical insulation layer is essential here as well.
A compact, visually pleasing arrangement results, according to a tenth aspect of the invention, if all antenna surface elements have an identical right-angled surface and are connected in parallel in a symmetrical arrangement with short lengths of supply lines.